The long-term objectives of this research program are to understand how temporal patterns in communication sounds are represented and processed in the central auditory system. Much of the information in communication signals, including human speech, resides in their temporal structure, and deficits in processing temporal information underlie disorders in speech recognition. An understanding of how the temporal structure of sounds is represented and processed in the nervous system is vital, therefore, to understanding the neural bases of communication and communicative disorders. The research will be conducted on the auditory system of anurans because the temporal structure of their vocalizations has been shown to be important in their reproductive biology, and they are well suited for neurophysiological investigations of the mechanisms that underlie temporal processing. At a basic level, the temporal structure of sound consists of how its amplitude and frequency changes, i.e., is modulated, over time. The specific goals of this research project are to gain insight into how amplitude modulations, including pulse duration and rise time, are represented in the brain and the mechanisms that underlie transformations in these representations. In a number of vertebrate species, including mammals, there is a transformation from a periodicity coding of the rate of amplitude modulation to an AM filter representation;most neurons in the midbrain respond best over a particular range of AM rate, i.e., are band-pass. The mechanisms underlying this transformation are poorly understood.